With the development of various displays such as a Liquid Crystal Display (LCD), a touch screen is widely used as one of the most efficient input devices for an interface between a user and a display. Since the touch screen allows a user to visually and conveniently manipulate various devices, such as a computer, a mobile phone, a banking terminal, a game console, etc., using a user's finger or a touch pen, etc., the touch screen can be applied to various applications.
Generally, methods for implementing a touch screen include an electrical method and an optical method. The electrical method may provide a resistive film type touch screen or an electrostatic capacitive type touch screen. The resistive film type and electrostatic capacitive type touch screens are generally applied to small-sized touch screens since they require a high manufacturing cost and have technical limitations for manufacturing large-size touch screens.
The optical method may use an infrared matrix type, a camera-based type, or the like. The infrared matrix touch screen has been fabricated as a middle- or large-sized touch screen. However, as the screen size of a touch screen increases, the touch screen consumes more power, requires a higher manufacturing cost, and is exposed to a higher risk of wrong operations due to surrounding conditions, such as sunlight, lighting, etc.
The camera-based touch screen is mainly fabricated as a large-sized touch screen. The camera-based touch screen may calculate location coordinates of a touching object on the basis of angles of images of the touching object captured by two cameras. The camera-based touch screen is also, like the infrared matrix touch screen, exposed to a high risk of wrong operation due to surrounding conditions, such as sunlight, lighting, etc., and may make an error in detecting the exact coordinate of touch point when a large object approaches the touch screen.
Especially, since a conventional touch sensing camera uses a circular lens, the larger aperture of the circular lens, the higher height of the camera disposed vertical to the touch surface. Furthermore, an image sensor is arranged in a standing position behind the camera lens in the direction of optical axis, this adds a further limitation in lowering the height of the camera disposed vertical to the touch surface. Accordingly, there are difficulties in installing cameras having the above-described configuration in a small- or middle-sized display, such as a LCD monitor for a desktop, a LCD monitor for a notebook, etc.